1. Field of the Invention
The present invention relates to defect detectors for detecting whether corrugated cardboard flutes (columns) are higher than or lower than an allowable range.
2. Description of Related Art
In the manufacture of corrugated cardboard sheets, at a step of forming a medium base paper into a corrugated shape and laminating the corrugated medium to a liner, a defective portion such as a crushed flute mountain (flute crush), an inclined flute mountain (flute inclination), or a projecting flute mountain (flute projection) caused by partial detachment of the corrugated medium from the liner or the like may be generated, which results in unevenness in thickness of the corrugated cardboard sheet. The present applicant has proposed a method of detecting the occurrence of this above-described defect by means of a method wherein flutes are examined on the manufacturing line during production of cardboard sheets, rather than after production is complete (See Patent Document 1).
This method is a method in which “a limited distance sensor for detecting that an object to be detected is positioned on an effective line of an inspection light is used, the effective line is set to a length approximately equal to one pitch of corrugated cardboard flutes, an inspection light is slightly inclined so that a tip of a normal flute mountain is positioned on or slightly under the posterior end of the effective line and simultaneously a slope of an adjacent normal flute mountain is positioned on the anterior end side of the effective line, normalcy is detected from the fact that normal mountains of traveling flutes are constantly positioned on a part of the effective line, abnormality of a flute mountain higher than a standard flute height is detected from the fact that a high flute mountain passes the inspection light on the sensor side outside the posterior end of the effective line, and abnormality of a flute mountain lower than the standard flute height is detected from the fact that a flute does not exist on the effective line because a slope of a low mountain does not reach the anterior end of the effective line when the previous mountain is positioned outside the posterior end of the effective line”.
Conventionally, the method has been realized by a detector including an optical projector for projecting to traveling flutes an inspection light inclined to graze a flute tip of a normally corrugated medium and reach a slope of an adjacent normal flute mountain thereto, and an optical receiver for detecting whether a light is received or not within a light-receiving range capable of receiving only the inspection light reflected by a flute mountain on the effective line.
According to such a detector, when the heights of flute mountains are within the allowable range, the inspection light projected by the optical projector is constantly reflected on the effective line and is received by the optical receiver. On the other hand, when the height of any flute mountain is higher than the allowable range, the inspection light is reflected by the flute mountain outside the posterior end of the effective line, so the optical receiver does not receive the inspection light. Further, when the height of any mountain is too low to reach the allowable range, the inspection light is reflected by the flute mountain outside the anterior end of the effective line, so the optical receiver does not receive the inspection light similarly.
Therefore, while the light is being detected by the optical receiver, it can be determined that the height of a flute is within the allowable range, and while the light is not detected by the optical receiver, it can be detected that either defect (i.e., the height of a flute is higher or lower than the allowable range) has been generated. That is, without requiring actual measurement of the height of a flute, whether the height of the flute is normal or not can be detected easily by detecting whether the optical receiver receives the inspection light or not.    [Patent Document 1] Japanese Patent No. 2571520